1. Field
The present disclosure relates to polymer blends and organic light-emitting diodes including the polymer blends.
2. Description of the Related Art
Organic light-emitting diodes (“OLEDs”) can be classified into small molecule OLEDs and polymer OLEDs according to the types of organic materials. In small molecule OLEDs, a thin film is prepared by vacuum deposition of a low molecular weight organic material. Small molecule OLEDs consist of materials that have well-known properties and relatively long lifetimes. However, since manufacturing costs of small molecule OLEDs are high, it is expensive to manufacture them on a large scale. On the other hand, in polymer OLEDs, a thin film is prepared from a high molecular weight organic material, i.e., a polymer, by using a solution coating process such as spin coating or inkjet printing. Polymer OLEDs have relatively short lifetimes, and high mechanical strength. They are manufactured by simplified processes, and may be conveniently prepared on a large scale. While technological advances in the development and use of small molecule OLEDs has been rapid, it has been much slower for polymer OLEDs.
There are several types of polymer emission layers. One type is a polymer emission layer that consists of a copolymer of hole transporting monomers, electron transporting monomers, and light-emitting monomers. Such a copolymer emission layer has bipolar properties (i.e., capable of transporting both holes and electrons) and emits lights from excitons generated by a current. The advantage of this type of the polymer emission layer is that since a single polymer has all the functions of the emission layer, a uniform film may be easily formed. However, in order to change electrical and optical properties of the polymer emission layer, a new polymer possessing desired characteristics needs to be designed and synthesized. Another type of a polymer emission layer is produced by blending small molecules and polymers, for example, by mixing light-emitting small molecules with a polymer possessing bipolar properties. However, with the increase in the ratio of small molecules to a polymer, phase separation may occur, thus making the use of such polymer emission layer difficult.